1. Technical Field
The present disclosure relates to enhanced spectrophotometer systems and subassemblies/components associated therewith. More particularly, the present disclosure relates to spectrophotometer systems and subassemblies/components thereof that provide and/or facilitate: (i) simultaneous measurement of “specular included” and “specular excluded” reflectance properties of a sample through an innovative zoom lens assembly; (ii) transmission measurements of virtually unlimited areas of interest through an innovative zoom lens assembly; (iii) automated and reliable determinations of the type of aperture plate placed at the front of the spectrophotometric instrument through an innovative aperture plate detection assembly; and (iv) reliable and non-disruptive sample placement through an innovative sample holder assembly.
2. Background Art
The use of integrating spheres as an optical measurement geometry in reflectance colorimetry is a standard practice, and is described in the Commission Internationale De L'Eclairage (CIE) Publication Number 15.2 (Colorimetry), 1986, the disclosure of which is hereby incorporated by reference herein. An integrating sphere is a hollow metal sphere, generally several inches or more in diameter, that is coated with a highly reflecting diffuse material, e.g., barium sulfate or polytetrafluoroethylene. Thus, an integrating sphere generally defines an interior cavity (typically spherical) having a highly reflective, optically diffuse white surface.
The simplest integrating sphere designs contain two apertures, one which admits light and another which serves as a measurement port where the amount of light on the surface of the sphere can be measured. The integrating sphere generally collects all the light reflected from the surface of a sample placed against an opening into the sphere. At any point on the inner surface of the sphere, the illumination is essentially independent of the direction and location of the incident beam as well as the size of the beam; the inner surface is uniformly illuminated throughout, except at the point of direct illumination. By placing a specular port at an opposite angle (relative to the normal angle offset), the specular reflection can be either included or excluded from the measurement by placing material identical to the sphere's interior or a black trap, respectively, at the specular port. Integrating spheres are generally used in colorimetry for the precise determination of color for a sample under test.
It is a common practice in colorimetry to measure a sample with the specular component of reflection (mirror-like reflection from the surface) either included (SCI mode) or excluded (SCE mode). Other measurement-related parameters may include selection of the size of the measured sample surface, spectral content of the illumination, and angle of receiver beam with respect to the sample normal. Historically, instruments designed for colorimetry have measured the sample one configuration at a time (e.g., SCI or SCE mode with a single size of measured area), usually requiring a change of configuration or another instrument to select another mode combination. In such instruments, the integrating-sphere calorimeter is generally capable of measuring the sample with the specular component either included or excluded. Changing between SCI and SCE modes is usually achieved by the use of a movable segment of the integrating sphere which removes the specular component for SCE measurements or includes the specular component for SCI measurements. In such an instrument, the included/excluded option requires separate measurements with a time between to move the segment and mechanical means to do so.
Many instruments are capable of selecting the size of the area of the sample surface to be measured. Size selection is usually done with a “zoom” optical system or movable lens(es)/aperture(s). In such instruments, changing the size of the measurement area generally requires separate measurements with an inherent delay associated with moving the lens(es)/aperture(s). Mechanical structures for repositioning the lens have also been provided. Many instruments also use a second optical path as a reference measurement to normalize/compensate for changes in the illumination. Such common practice is generally referred to as “dual beam” optics.
Certain commercially available spectrophotometers in the color industry incorporate a method by which aperture plates corresponding to different aperture sizes are detected or selected so that the instrument can be properly configured to make the desired measurement with respect to the optical properties of the system in order to measure the correct area of interest. However, current methodologies for automatic aperture plate detection disadvantageously require a specific orientation of the aperture plate and typically use an optical sensor to determine the presence of a plate and the plate type. Commercially available methodologies for aperture plate detection are unacceptably limited and unreliable.
Bench top spectrophotometers in the color industry generally use a sample holder device to secure the sample under test to-the instrument. Typical commercial systems are constructed using an “over-centered spring” design which allows the “sample arm” to be pulled away from the instrument (thus releasing the sample under test) and to maintain its open state once the “over-centered” position is reached. A major draw back to the foregoing “over-center” design is that, once the sample arm is moved from the “over-centered” position, it “mouse-traps” or springs back on the sample with great force. This force is frequently sufficient to damage the delicate coating of the illumination sphere in the area where the sample is typically placed, thereby imparting undesirable damage to the instrument and an attendant cost and interruption in use to the system user.
Colorimetry instruments with multiple measurement paths, e.g., measurement paths for simultaneously measuring sample SCI and SCE, are known. For example, U.S. Pat. No. 5,369,481 to Berg et al. discloses a portable spectrophotometer that includes a small-diameter optical sphere as well as optical detectors and signal processing and display circuitry which allow the instrument to be taken to an object to be measured and which provide a readout of color values at the portable instrument. The instrument is capable of providing specular-included and specular-excluded color readings simultaneously. The sphere is provided with a first aperture which receives spectrally-included light and which is positioned to absorb a spectral component of the diffused source light. A second aperture positioned at a corresponding angular position with respect to the object measures specular-excluded light, excluding the specular component absorbed by the first aperture. Light detected from the first aperture is analyzed at a plurality of wavelengths obtained by the use of interference filters, and the light obtained from the second aperture is analyzed at one of the plurality of wavelengths. By combining the specular-included and specular-excluded at one wavelength, a value for the specular component is derived. Since this value is a theoretical constant, it is used to derive a specular-excluded reading from each of the specular-included readings at the different wavelengths.
Commonly assigned U.S. Pat. No. 6,424,413 to Weber et al. describes a multi-channel integrating sphere and an integrating sphere-based reflectance colorimeter/spectrophotometer for the measurement of color and appearance The Weber '413 patent discloses devices that include multiple receivers capable of concurrently receiving optical radiation scattered/reflected from a diffusely illuminated sample surface, with the capability of multiple measurement modes (e.g., multiple specular component excluded (SCE), SCE and specular component included (SCI), multiple SCI), multiple areas-of-view for a given measurement mode, multiple viewing angles per measurement mode, and combinations thereof. In a disclosed embodiment, two SCI receivers and two SCE receivers are provided, each disposed at an equal viewing angle relative to the sample surface. For each viewing mode, two sample areas-of-view are provided. The SCE receivers are opposite each other, such that the specular component of each SCE receiver is excluded by the port of the other SCE receiver. The receivers provide the collected light reflected from the sample to a detector which preferably is provided by multiple spectrometers or a single spectrometer having multi-channel capability to preferably sense the light from each receiver in parallel. The entire contents of the Weber '413 patent are hereby incorporated herein by reference.
Despite efforts to date, a need remains for enhanced colorimetric/spectrophotometric systems and subassemblies/components thereof having certain desirable features and functionalities. In particular, a need remains for colorimetric/spectrophotometric systems and subassemblies/components thereof that provide enhanced zoom lens functionalities and/or capabilities, enhanced aperture plate-detection functionalities and/or capabilities, and/or enhanced sample placement functionalities and/or capabilities.
These and other advantageous features, functionalities and capabilities are provided according to the advantageous colorimetric/spectrophotometric systems and subassemblies/components thereof that are disclosed herein.